The concept of flow valves such as booster valves is well known in the art. Typically, booster valves are used in pneumatic conveying systems to increase the energy of the fluid in a conveying line by inserting a fluid, such as air at a higher pressure than the air in the conveying line, which assists in transporting materials through the conveying lines. Examples of such booster valves can be found in Steele U.S. Pat. Nos. 4,313,699; 4,708,535 and 5,345,969.
The booster valves need to withstand a hostile environment and be able to operate over an extended period of time as well as to prevent back low through the valve. In addition, in some circumstances it is desired to have the booster valve respond to extremely low differential pressure conditions. The present invention provides an improved flow valve or booster valve that has a sealing member that provides two conditions of operation, a flow condition and a no-flow condition. The booster valve includes a disk-like sealing member that cantilevers radially outward with a continuous annular peripheral region that flexes to engage an annular sealing surface on the interior of a housing when the pressures are equal on both sides of the sealing member. The partial engagement of the sealing member with the annular sealing surface in the housing is sufficient to prevent backflow at low pressure differentials. If the backflow pressure increases the central portion of the disk-like sealing member is displaced upward to further block off the internal fluid ports, which are located radially inward from the annular sealing surface on the interior of the housing. However, should the pressure differential across the booster valve drop to a displacement differential pressure condition the central portion of the disk-like sealing member and the cantilever portion of the sealing member engaging the annular sealing surface are axially displaceable and are supported in an out-of-the-way condition on a support platform. As a result, if air is used as the fluid, air can be added to the conveying line almost as soon as the pressure in the conveying line begins to drop. Thus, in one stage of operation the entire sealing member can seal off the fluid inlet ports and in another stage of operation a bias seal is formed by the resiliency of the sealing member. If the upstream pressure exceeds the downstream pressure the pressure on the sealing member by the fluid in the flow valve brings the sealing member to an out-of-the-way and supported condition that allows fluid to quickly flow through the flow valve.